This invention relates to a process for the production of pure cyclopentene.
It is known to obtain cyclopentene from diolefin-containing hydrocarbon mixtures, e.g., pyrolysis benzines or cracked gasoline containing cyclopentene, cyclopentadiene and/or dicyclopentadiene by selectively hydrogenating the diolefins in the hydrocarbon mixture to monoolefins and isolating the cyclopentene by distillative separation, e.g., see German Unexamined Laid-Open Application DOS 1,643,947,
Furthermore, it is known from DOS 1,793,254 to obtain cyclopentene, together with isoprene and a diolefin stream containing essentially 1,3-pentadiene and cyclopentadiene, from C.sub.5 -hydrocarbon mixtures by subjecting the hydrocarbon mixture to a liquid-liquid extraction with 1-oxo-1-methyl-phospholine as the selective solvent, in combination with an extractive distillation. DOS 1,793,256 likewise describes a process for the separation of C.sub.5 -hydrocarbon mixtures and for obtaining polymerizable cyclopentene, using N-methyloxazolidone as the selective solvent.
It is furthermore known from DOS 1,793,273 to separate the selective solvent, after liquid-liquid extraction and extractive distillation, in a liquid-liquid counter extraction from the C.sub.5 -diolefins with a second solvent and to employ a portion of the C.sub.5 -hydrocarbon vapors at the head of the distillation column for separation of the second solvent from the diolefins to operate the extractive distillation stage.
DOS 2,025,411 describes the production of cyclopentene from cyclopentadiene by partial hydrogenation with molecular hydrogen in the gaseous phase at temperatures of above 50.degree.C with a supported hydrogenation catalyst containing palladium as the active component with additives of chromium and/or titanium.
Finally, it is known from DOS 2,131,791 to treat cyclopentene containing olefinic and diolefinic C.sub.5 -hydrocarbon impurities with an acidic cation exchanger and thereafter to separate cyclopentene from the thus-obtained product by means of distillation.
All of the above-described processes in the present state of the art presuppose the isolation of cyclopentadiene-cyclopentene mixtures from C.sub.5 -cuts, which are commercially available only in limited amounts so that quantitative production of cyclopentene is limited. A further disadvantage of such processes is that economical isolation of the cyclopentene is possible only in conjunction with simultaneous exploitation of the isoprene component of the C.sub.5 -cut. A usable quality of cyclopentene is obtained only by way of several stages, some of which are technologically complicated. Furthermore, since a complete lack of diene in the cyclopentene, desirable for a polymerization of the cyclopentene with the aid of so-called metathesis catalysts, is not ensured in the prior art processes, there is often an increased consumption of catalyst during polymerization. This, in turn, leads to either more expensive working-up processes or to an increased ash content in the polymers.
U.S. Patent Application Ser. No. 465,515 describes a process for the preparation of pure cyclopentene wherein cis, cis-1,6-cyclodecadiene is reacted with a metathesis catalyst, optionally in the presence of a solvent, at temperatures of above 0.degree.C.
In a further development of this process, it has now been found that pure cyclopentene can be produced by employing a heterogeneous metathesis catalyst comprising
a. a support material and
b. an oxide of the elements of Group VI A or VII A of the Mendeleyev Periodic Table of the elements.